1. Field of the Invention
The invention relates to seats with adjustable-tilt back-rests, notably for vehicles.
2. Description of the Prior Art
In general the back-rests of these seats are mounted to pivot around a transverse axle positioned in the rear lower zone of the seat and means are provided to lock the back-rest in a certain number of distinct angular positions around the axle.
This solution necessitates recourse to parts (shafts, bearings, pins. . . ) which must be machined accurately and must have high mechanical strength in order to withstand the forces concentrated in the vicinity of the axle: hence these parts are relatively expensive.
Such a solution not being applicable to seats of which at least the seat-bottom framework is constituted by a shell, the present inventor has quite recently had the idea of constructing the articulation of the seat-back, in this particular case, by means of additional curvilinear slide elements centered on the same transverse axle advantageously situated in the vicinity of the pivoting axis of the hips of the person sitting on the seat, said elements being borne, on each side of the seat, respectively by the rear portions of vertical wings of the seat-bottom shell and by the bases of vertical side flanges of the back-rest.
The slide elements concerned were then constituted essentially by concentric grooves and ribs forming respectively hollows and projections on said wings and tabs.
The latter construction principle has notable advantages (lightness, simplicity of manufacture, economy . . . ) due to the fact notably of the distribution of the forces over relatively extended bearing surfaces.
Another object of the invention is to eliminate the usual pivoting axis and the "hard point" that its presence frequently creates at the back of the seat-bottom cushion.
Another object is to provide such a seat of which it is relatively easy to adjust the seat-back tilt by the cooperation of at least one curved rack centered on the transverse axis of the slides and fast to one of the two frameworks with at least one rotary toothed member easily actuatable by the seated person and mounted on the other framework.
It is another object of the present invention to apply the above construction principle to seats the seat-bottom and back-rest frameworks of which are in the general shape of frames constituted by metal bracing elements.
The invention relates more particularly to those seats of the type concerned, of which the framework of the back-rest comprises two incurved metal sectional bars arranged respectively on the two sides of the back-rest, each extending downwardly and forwards the base of one of the sides of this back-rest and centered on the same horizontal transverse axle situated in the vicinity of the pivoting axis of the hips of the person sitting on the seat, these sectional bars being adapted to coact with guide members of the seat bottom and means being provided to adjust the relative positions of the sectional bars with respect to the guide members and to block them in a plurality of distinct mutual positions.
In known embodiments of such seats, constituting office chairs, the sectional bars are constituted by curved tubes and the guide members are constituted, for each tube, by two pairs of rollers.
Such a construction is not sufficiently robust to be applied to a vehicle seat.